I. Field of the Invention
This invention relates to a process for the preparation of liquid hydrocarbons from methanol. In particular, it relates to a process wherein C.sub.10 + distillate fuels and other valuable products are prepared by reaction of methanol, and hydrogen, over a ruthenium catalyst.
II. The Prior Art
Methane is often available in large quantities from process streams either as an undesirable by-product in admixture with other gases, or as an off gas component of a process unit, or units. More importantly, however, methane is the principle component of natural gas, and it is produced in considerable quantities in oil and gas fields. The existence of large methane, natural gas reserves coupled with the need to produce premium grade transportation fuels, particularly middle distillate fuels, creates a large incentive for the development of a new gas-to-liquids process. Conventional technology, however, is not entirely adequate for such purpose. Nonetheless, technology is available for conversion of synthesis gas, which can be obtained from coal or natural gas, to produce methanol, a product of currently limited marketability. However, to utilize the existing technology, there is a need for a process suitable for the conversion of methanol to high quality transportation fuels, particularly middle distillate fuels.
III. Objects
It is, accordingly, a primary objective of the present invention to supply this need.
A particular object is to provide a novel process useful for the conversion of methanol to admixtures of C.sub.10 + linear paraffins and olefins which can be further refined and upgraded to high quality middle distillate fuels, and other valuable products.
A particular object is to provide a process as characterized, useful in combination with an upstream conventional methanol synthesis plant.
IV. The Invention
These objects and others are achieved in accordance with the present invention embodying a process wherein methanol is contacted, in the presence of hydrogen, over a ruthenium-titania catalyst to produce, at reaction conditions, an admixture C.sub.10 + linear paraffin and olefins, which can be further refined and upgraded to high quality middle distillate fuels, and other valuable products such as mogas, diesel fuel, jet fuel, lubes, and specialty solvents, especially premium middle distillate fuels of carbon number ranging from about C.sub.10 to C.sub.20.
The ruthenium-titania catalyst is one wherein ruthenium is composited, or dispersed upon titania (TiO.sub.2), or a titania-containing carrier, or support. The ruthenium is dispersed on the support in catalytically effective amounts. Suitably, in terms of absolute concentration, the ruthenium is dispersed on the support in amounts ranging from about 0.01 percent to about 8 percent, preferably from about 0.2 percent to about 4 percent, based on the total weight of the catalyst composition. These catalyst compositions, it has been found, produce at reaction conditions a product which is predominantly C.sub.10 + linear paraffins and olefins, with very little oxygenates. These catalysts provide high selectivity, high activity and good activity maintenance in the conversion of methanol to C.sub.10 + hydrocarbons.
In conducting the reaction the total pressure must be maintained above about 160 pounds per square inch gauge (psig), and preferably above about 225 psig, and it is generally desirable to employ methanol, and hydrogen, in molar ratio of CH.sub.3 OH:H.sub.2 of at least about 2:1 and preferably at least about 4:1 to increase the concentration of C.sub.10 + hydrocarbons in the product. Suitably, the CH.sub.3 OH:H.sub.2 molar ratio ranges from about 2:1 to about 50:1, and preferably the methanol and hydrogen are employed in molar ratio ranging from about 4:1 to about 40:1. In general, the reaction is carried out at liquid hourly space velocities ranging from about 0.1 hr.sup.-1 to about 10 hr.sup.-1, preferably from about 0.2 hr.sup.-1 to about 2 hr.sup.-1, and at temperatures ranging from about 150.degree. C. to about 350.degree. C., preferably from about 180.degree. C. to about 250.degree. C. Pressures range from about 160 psig to about 800 psig, preferably from about 225 psig to about 500 psig. The product generally and preferably contains 50 percent, or greater, C.sub.10 + liquid hydrocarbons which boil above about 160.degree. C. (320.degree. F.).
Ruthenium/titania catalysts exhibit high activity and selectivity in the conversion of a feed consisting essentially of methanol, and hydrogen, to C.sub.10 + middle distillates. The catalysts employed in the practice of this invention may be prepared by techniques known in the art for the preparation of these and other catalysts. The catalyst can, e.g., be prepared by gellation, or cogellation techniques. Suitably, however, ruthenium can be composited alone, or with another metal, or metals, upon a previously pilled, pelleted, beaded, extruded, or sieved titania or titania-containing support material by the impregnation method. Suitably the ruthenium is composited with the support by contacting the support with a solution of a ruthenium-containing compound, or salt, e.g., a nitrate, chloride or the like. The amount of impregnation solution used should be sufficient to completely immerse the carrier, usually within the range from about 1 to 20 times the carrier by volume, depending on the concentration of the ruthenium-containing compound in the impregnation solution. The impregnation treatment can be carried out under a wide range of conditions including ambient or elevated temperatures. Metal components other than ruthenium may also be added as promoters. The introduction of another metal, or metals, into the catalyst can be carried out by any method and at any time of the catalyst preparation, for example, prior to, following or simultaneously with the impregnation of the support with the ruthenium component. In the usual operation, the additional component is introduced simultaneously with the incorporation of the ruthenium component.
The catalyst, after impregnation, is dried by heating at a temperature above about 25.degree. C., preferably between about 65.degree. C., and 150.degree. C., in the presence of nitrogen or oxygen, or both, in an air stream or under vacuum. The metal, or metals, contained on the catalyst can then be reduced. Reduction is performed by contact of the catalyst with hydrogen or a hydrogen-containing gas stream at temperatures ranging from about 180.degree. C. to about 575.degree. C. for periods ranging from about 0.5 to about 24 hours at pressures ranging from ambient to about 40 atmospheres. A gas containing hydrogen and inert components, or a gas containing hydrogen and carbon monoxide in admixture are satisfactory for use in carrying out the reduction.
The invention will be more fully understood by reference to the following demonstrations and examples which present comparative data illustrating its more salient features.
The data given in the examples which follow were obtained in a small fixed bed reactor unit, conventional material balance work-up having been obtained during the runs which were conducted over 24 to 100 hour periods. All parts are in terms of weight units except as otherwise specified.
The "Schulz-Flory Alpha" is a known method for describing the product distribution in Fischer-Tropsch synthesis reactions, and it is also useful in describing the product distribution from methanol conversion reactions. The Schulz-Flory Alpha is the ratio of the rate of chain propagation to the rate of propagation plus termination, and is described from the plot of 1n (Wn/n) versus n, where Wn is the weight fraction of product with a carbon number of n. In the examples below, an Alpha value was derived from the C.sub.10 /C.sub.20 portion of the product. The Alpha value is indicative of the selectivity of the catalyst for producing heavy hydrocarbons from the methanol, and is indicative of the amount of C.sub.10 + hydrocarbons in the product. For example, a Schulz-Flory Alpha of 0.80 corresponds to about 35% by weight of C.sub.10 + hydrocarbons in the product, a generally acceptable level of C.sub.10 + hydrocarbons. A Schulz-Flory Alpha of 0.85, a preferred Alpha value, corresponds to about 54% by weight of C.sub.10 + hydrocarbons in the products, and a Schulz-Flory Alpha of 0.90, a more preferred Alpha value, corresponds to about 74% by weight of C.sub.10 + hydrocarbons in the product.
The ruthenium-titania catalysts used in the examples below were prepared by the following procedure:
Titania (Degussa P-25 TiO.sub.2) was used as the support after mixing with sterotex, and after pilling, grinding, and screening to 80-150 mesh (Tyler). The titania was calcined in air and reduced with H.sub.2 at 500.degree. C. to provide a support containing a rutile:anatase ratio of 2:1 (ASTM D 3720-78: Standard Test Method for Ratio of Anatase to Rutile in Titanium Dioxide Pigments by Use of X-Ray Diffraction) with a surface area of 23 m.sup.2 /g and a pore volume of 0.24 ml/gm. Catalysts, of 80-150 mesh size, were prepared by simple impregnation of the support with ruthenium nitrate (Engelhard) from acetone solution using a rotary evaporator, drying in a vacuum oven at 150.degree. C. These catalysts were charged to a reactor, reduced in H.sub.2 at 450.degree. C. for one hour, and then reacted with methanol at the conditions described in the examples .